- NMR and DFT studies on persistent carbocations derived from benzo[kl]xanthene, dibenzo[d,d′]benzo[1,2-b:4,3-b′]difuran, and dibenzo[d,d′]benzo[1,2-b:4,5-b′]difuran in superacidic media
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Persistent carbocations generated by the protonation of hetero-polycyclic aromatic compounds with oxygen atom(s) were studied by experimental NMR and density function theory calculations. Benzo[kl]xanthene (1), dibenzo[d,d′]benzo[1,2-b:4,3-b′]difuran (2), and dibenzo[d,d′]benzo[1,2-b:4,5-b′]difuran (3) were synthesized by the annulation of arenediazonium salts. Compound 1 in FSO3H-SbF5 (4:1)/SO2ClF and 3 in FSO3H-SbF5 (1:1)/SO2ClF ionized to 1aH+ with protonation at C(4) and to 3aH+ with protonation at C(6), and these cations were successfully observed by NMR at low temperatures. The density function theory calculations indicated that 1aH+ and 3aH+ were the most stable protonated carbocations and that 2 should ionize to 2aH+ with protonation at C(6). According to the changes in 13C chemical shifts (Δδ13C), the positive charge was delocalized into the naphthalene unit for 1aH+, into one benzo[b,d]furan unit for 2aH+, and into one benzo[b,d]furan unit for 3aH+. The most stable persistent cations derived from the title compounds, 1-3, were found to be 1aH+ with protonation at C(4), 2aH+ with protonation at C(6), and 3aH+ with protonation at C(6) by experimental and theoretical methods.
- Okazaki, Takao,Nakagawa, Madoka,Futemma, Takeshi,Kitagawa, Toshikazu
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supporting information
p. 107 - 111
(2016/02/03)
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- Palladium Acetate-Mediated Cyclizations of Di- and Trifunctional Triarylamines, Diaryl Ethers, and Diaryl Ketones
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Triphenylamine and its 4,(4',4")-substituted nitro or ester and methyl derivatives are cyclodehydrogenated to the corresponding carbazole derivatives 4a-d with Pd(OAc)2 in acetic acid.Further cyclizations can not be observed.Multiple cyclizations of this kind, however, can be realized with compounds of the 1,4-diphenoxybenzene (6a), 1,4-dibenzoylbenzene (6b), and 2,8-diphenoxydibenzofuran type (10), where in a very simple manner benzobisbenzofurans 8a, 9a, indenofluorene-6,12-dione (8b), 11H-fluorenobenzofuran-11-one (8c), and bisbenzofurodibenzofuran (12) become accessible.
- Hellwinkel, Dieter,Kistenmacher, Thomas
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p. 945 - 950
(2007/10/02)
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